Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$18.61	7.723%	$20.0473	$20.05	$20.05	$20.00
Purchase #2	$208.26	4.144%	$216.8903	$216.89	$216.90	$216.90
Purchase #3	$130.79	9.575%	$143.3131	$143.31	$143.30	$143.30
Purchase #4	$91.59	10.607%	$101.305	$101.31	$101.30	$101.30
Purchase #5	$237.41	3.289%	$245.2184	$245.22	$245.20	$245.20
Purchase #6	$121.41	5.674%	$128.2988	$128.30	$128.30	$128.30
Purchase #7	$56.70	5.608%	$59.8797	$59.88	$59.90	$59.90
7 purchase totals =	$864.77		$914.9526	$914.96	$914.95	$914.90